Scrapie of sheep and goats is the most common prion disease (or transmissible spongiform encephalopathy, TSE) of mammals and aggregates of abnormal, proteinase-resistant prion protein (PrP Sc) are found in all naturally occurring prion diseases. During active surveillance of British sheep for TSEs, 29 201 sheep brain stem samples were collected from abattoirs and analysed for the presence of PrP Sc. Of these samples, 54 were found to be positive by using an ELISA screening test, but 28 of these could not be confirmed initially by immunohistochemistry. These unconfirmed or atypical cases were generally found in PrP genotypes normally associated with relative resistance to clinical scrapie and further biochemical analysis revealed that they contained forms of PrP Sc with a relatively protease-sensitive amyloid core, some resembling those of Nor98 scrapie. The presence of these atypical forms of protease-resistant PrP raises concerns that some TSE disorders of PrP metabolism previously may have escaped identification in the British sheep population.

The role of blood in the iatrogenic transmission of transmissible spongiform encephalopathy (TSE) or prion disease has become an increasing concern since the reports of variant Creutzfeldt-Jakob disease (vCJD) transmission through blood transfusion from humans with subclinical infection. The development of highly sensitive rapid assays to screen for prion infection in blood is of high priority in order to facilitate the prevention of transmission via blood and blood products. In the present study we show that PrP sc , a surrogate marker for TSE infection, can be detected in cells isolated from the blood from naturally and experimentally infected sheep by using a rapid ligand-based immunoassay. In sheep with clinical disease, PrP sc was detected in the blood of 55% of scrapie agent-infected animals (n ‫؍‬ 80) and 71% of animals with bovine spongiform encephalopathy (n ‫؍‬ 7). PrP sc was also detected several months before the onset of clinical signs in a subset of scrapie agent-infected sheep, followed from 3 months of age to clinical disease. This study confirms that PrP sc is associated with the cellular component of blood and can be detected in preclinical sheep by an immunoassay in the absence of in vitro or in vivo amplification.

Classical scrapie is a naturally transmitted prion disease of sheep and goats. Contaminated environments may contribute to the spread of disease and evidence from animal models has implicated urine, blood, saliva, placenta and faeces as possible sources of the infection. Here we sought to determine whether sheep naturally infected with classical scrapie shed prions in their faeces. We used serial protein misfolding cyclic amplification (sPMCA) along with two extraction methods to examine faeces from sheep during both the clinical and preclinical phases of the disease and showed amplification of PrPSc in 7 of 15 and 14 of 14 sheep respectively. However PrPSc was not amplified from the faeces of 25 sheep not exposed to scrapie. These data represent the first demonstration of prion shedding in faeces from a naturally infected host and thus a likely source of prion contamination in the environment.

Development of immunoassays with broad speci®city recognition of the sulphonamide drugs has proved surprisingly dif®cult in previous work. We have taken an antiserum speci®c for sulphachlorpyridazine in an ELISA system homologous for immunogen and solid phase conjugate and used it in a heterologous ELISA format. The assay proved to have broad speci®city, recognising 15 out of 21 drugs tested. Despite low cross-reactivity (<1%) for seven of the drugs tested, a fully optimised assay could prove useful as a multiresidue method for the group of drugs. The results provide evidence regarding the binding characteristics of the antibody and the immunogenicity of the target.

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